Ben Beach (above), 63, was aiming to run his 46th consecutive Boston Marathon this year, which would put him atop the all-time list of Quarter Century Club members (runners who've completed at least 25 Bostons in a row).

But two days before the marathon, on an easy run, he felt a twinge in his calf. He dismissed it as a symptom of the 'taper crazies,' and lined up with the third wave as planned.

About a mile in, he started to feel the ache again, and it got progressively worse. After mile 10—sudden, intense pain. "It was a minor tear," he says, "but it didn't feel very minor. It was clear I was not going to be able to run on the thing."

With his hopes for a 4:30 finish dashed, he calculated that he'd have to walk the rest of the race at 15 minute per mile pace to arrive before the six-hour course time limit. That became his race plan.

When he was going through the Newton hills, he overheard a spectator claiming a pair of explosions had taken place at the finish line. "That was just a mind-blowing thought," he says. "I was skeptical that it could really have happened." A few minutes later, a string of police, on motorcycles and in cars, flew by with their sirens blaring. Clearly, something was going on.

Near Boston College, volunteers blocked the road and told the runners they had to stop. They gave him ice for his injury, and a space blanket to keep warm. News was filtering through the group: two dead, 20 injured (at that time).

Beach was able to find his kids, who'd been watching nearby, and they reached his wife using his son's cell phone. For the first time, she'd had tickets for the finish-line bleachers, but she hadn't made it there—she saw her injured husband at mile 16 and knew he wouldn't be finishing for a while.

"You don't like to get an injury, but this was the perfect day to get one," he says. "Had I been on schedule, she very likely would have been down there."

He'll be back to run the race next year. "That didn't require any thought at all," he says.

In the meantime, he, and other members of the Quarter Century Club who were stopped on the course await the B.A.A.'s verdict on whether they'll be issued finishing times based on their progress before the blasts.

"I regret that I was unable to reach the finish line, but that pales in comparison to how everybody who was really hurt by this feels," Beach says.

Here's how other top Quarter Century Club members fared:Timothy Lepore, 68: En route to his 45th consecutive Boston. Was stopped at the 30K mark.Mark Bauman, 63: En route to his 44th consecutive Boston. Was stopped at the 40K mark.Dave McGillivray, 58: The Boston Marathon race director has run the course late in the day for the last 40 years. He completed his 2013 run on April 26.Russell Gill, 61: He finished his 40th consecutive Boston in 3:52:52. He was the highest person on the QCC list to complete the race.